The so-called electric sliding mechanism is a mechanism in which two different electric parts come into contact with each other and slide while conducting electricity between them. The electric sliding mechanism, which is represented by a collecting brush and a slip ring of a generator, is used in various products. It is essential that the electric sliding mechanism be inspected and replaced as needed because a relevant electric part (the collecting brush in the current example) gradually wears.
However, the electric parts variously wear depending on ambient environmental conditions and load changes so that their wear rate varies. Further, as the electric parts differ in the flow of an electric current, the wear rate may vary from one electric part to another. Therefore, if the sliding condition of each electric part is left uninspected, the electric sliding mechanism may stop functioning to cause a serious accident. If, for example, abnormal sliding occurs between the collecting brush (fixed part) and slip ring (rotary part) of the generator, the generator becomes unavailable and entails a considerable maintenance cost due, for instance, to unexpected slip ring replacement.
Meanwhile, diagnosing the surface condition of the slip ring is effective for early detection of abnormal sliding in the power generator. However, the inspection of the surface condition, such as the inspection of gloss, hue, or surface irregularities, frequently depends on the experience of maintenance personnel who conducts a visual or tactile inspection. In reality, therefore, it is practically difficult to obtain an opportunity of allowing well-experienced maintenance personnel to achieve early detection of abnormal sliding.
As such being the case, a quantitative diagnostic technology for sliding surface inspection, which is not dependent on experience, is disclosed in Japanese Unexamined Patent Application Publication No. 2009-222575. A configuration described in Japanese Unexamined Patent Application Publication No. 2009-222575 receives light reflected from the surface of a commutator of an electric motor, extracts a specular reflection component from the reflected light, and compares the glossiness of the specular reflection component with a threshold value to detect abnormal sliding.
When, for instance, the collecting brush and the slip ring slide normally, the collecting brush and the slip ring, which have a curved surface, are sliding in substantially full contact with each other. Therefore, an electric current flows uniformly over a substantially entire surface.
Meanwhile, abnormal sliding occurs when the collecting brush jumps away from the slip ring for some reason or is placed in a biased position. In this state, an overcurrent flows over a portion of the surface of the collecting brush that is sliding in contact with the slip ring. Further, a small discharge, which occurs in an open condition in which the collecting brush and the slip ring come close to each other and go away from each other, occurs frequently.
In the event of the small discharge, the material of the collecting brush scatters and attaches to the surface of the slip ring. A metal graphite brush, which is mainly used as the collecting brush, is made of a copper-graphite alloy. As copper is lower in melting point and boiling point than graphite, the electric discharge tolerance of copper is weak. Therefore, in the event of the small discharge, the copper scatters and excessively attaches to the surface of the slip ring, thereby creating a copper-rich surface film condition.
In an abnormal sliding condition, it is understood that the above phenomenon gradually develops. Meanwhile, a method described in Japanese Unexamined Patent Application Publication No. 2009-222575 uses the glossiness of specular reflected light. However, when the glossiness is to be measured, only the intensity of specular reflected light from a sliding surface is quantified without making a wavelength selection. Thus, the aforementioned hue is not examined for identification. This makes it impossible to recognize the excessive attachment of copper, which is a phenomenon concomitant to abnormal sliding.
Further, to obtain the specular reflected light, it is necessary that a light source, which emits light, and a light-receiving section, which detects reflected light, be disposed line-symmetrically with respect to the normal line of the surface of the commutator (the angle of incidence and the angle of reflection be 20 degrees or 60 degrees). In reality, however, it is difficult to achieve such a positional relationship and obtain a desired result at an actual installation site. It is more difficult to achieve such a positional relationship at an installation site near the surface of a rotating body such as the slip ring.
The present invention has been made in view of the above circumstances and provides equipment and method for diagnosing the sliding condition of a rotating electrical machine that make it possible to achieve early detection of abnormal sliding with a simple configuration containing flexibly arranged elements and reduce the downtime and maintenance cost of the rotating electrical machine.